At present, a serious problem is in increasing an information transfer rate over paths consisting of lines having different nature. Generally, an information transfer path consists of pulse-code modulation (PCM) channel coupling automatic exchanges which are connected to modems of analogue line end users. Such an analogue (telephone, as a rule) line has been referred to specifically as the “last mile”.
Usual PCM channel has a bandwidth of 4 kHz and can transfer a 8-bit signal, which is equivalent to the transmission rate of 64 kbit/sec. An analogue line of the “last mile” transmits a signal occupied a bandwidth not more than 3.1 kHz and ensures, depending on the employed modulation type, a transmission rate of 300 to 14400 bit/sec at signal-to-noise ratio of 20 to 25 dB.
The relation between the rate C of information transmission over a communication line (channel), the bandwidth π of the communication line (channel), the power PC of a signal being transmitted, and the power Pπ of interference in the communication line (channel) is defined by the Shannon equation:
                    C        =                              Π            ·                          log              2                                ⁢                                                    P                C                            +                              P                Π                                                    P              Π                                                          (        1        )            For the analogue line having the bandwidth π=4 kHz and the ratio of signal power PC to the interference power Pπ (the signal-to-noise ratio) of 42 dB, the information transfer rate C=55.9 kbit/sec. This relation is deduced for the ideal case, and in practice a reserve is necessary of 7 to 8 dB, i.e., the signal-to-noise ratio will be approximately 50 dB. However, real analogue lines have the signal-to-noise ratio about 10 to 20 dB, which gives, according to the Equation (1), the rate C=15-30 kbit/sec.
Known are the method and system for duplex transmitting a discrete information over the PCM channel, which method and system ensure the data transmission from the PCM channel to the end user modem at the rate of 56 kbit/sec, but the data rate in the opposite direction in this method does not exceed 33.6 kbit/sec [ (E. B. Minkin). << <<56K- >> (Anatomy of modem “56K-technologies”)//Cemu u cucme (Communication networks and systems). 1997, No. 8, pp. 54-61, and No. 9, pp. 78-87 (in Russian)].
Disadvantage of the indicated prior art is in impossibility to increase the transfer path capacity due to the fact that the bandwidth of analogue line is generally chosen equal to the bandwidth of PCM channel, i.e., 4 kHz.
The closest analogue is the method for duplex transmitting a discrete information over a communication path comprising a bidirectional PCM channel, each end of which turns into a respective bidirectional analogue communication line, the method including steps of: converting samples of discrete signal to be transmitted to the form suitable for transmitting over a bidirectional analogue communication line; transmitting the converted signal samples over the analogue communication line to the PCM channel; converting a signal received from the analogue communication line into a PCM channel signal; transmitting the PCM channel signal over said PCM channel; performing the inverse conversion of channel signals after their passing over the PCM channel; transmitting the converted channel signals over another bidirectional analogue communication line; picking out the signals transmitted over the another bidirectional analogue communication line; and converting those signals into discrete samples [WO 01/99364, H 04 L 27/26, 27.12.2001].
The method for duplex transmitting over a single path could be imagined as an independent transmission of signals in opposite directions over two virtual paths. Then, the same document [WO 01/99364 A1] could be considered as disclosing the known method for transmitting a discrete information over a communication path comprising, in the direction of signal transmission, at least an analogue communication line and a PCM channel, the method including steps of: converting samples of discrete signal to be transmitted to the form suitable for transmitting over an analogue communication line; transmitting the converted signal samples over the analogue communication line to the PCM channel; converting a signal received from the analogue communication line into a PCM channel signal; transmitting the PCM channel signal over said PCM channel.
The method for duplex transmitting is realized using the system for duplex transmitting a discrete information, the system comprising: a first modem, a first bidirectional analogue communication line, a first converter, a bidirectional PCM channel, a second converter, a second bidirectional analogue communication line, and a second modem, all coupled in series [WO 01/99364 A1].
The method for transmitting a discrete information over a communication path comprising, in the direction of signal transmission, at least an analogue communication line and a PCM channel, could be realized using the system for transmitting a discrete information, the system comprising a modulator, an analogue communication line, a direct converter, and a PCM channel [WO 01/99364 A1].
The indicated document, as well as the co-pending PCT Application WO 01/99365 describe the method and system for transmitting a discrete information to be used in networks with data transfer rates of 64 kbit/sec at the signal-to-noise ratio 10 dB in a telephone line when transmitting from a subscriber to a PCM equipment. However, the analysis of both those PCT Applications reveals that, in order to realize the indicated data transfer rate, the conversion of information signal into eight low-frequency channels is used, each of which channels occupies a bandwidth of 0 to 4 kHz, the bandwidth of all eight channels being spread onto different frequencies to make, as a result, all channels to occupy a bandwidth of 32 kHz. In practice, due to a necessity of providing a required isolation between channels, the total bandwidth of all eight channels will be larger than 32 kHz; otherwise, it will have to reduce a bandwidth occupied by each channel, which leads to distortions of transmitted signal.